Method of making dense magnesium oxide



Nov. 23, 1948. A. D. DAI-u.

METHOD OF MAKING DNSE HAGHESIUM'OXIDE Filed laren v1s, 1947 Barni/7 9magnesium drops Liga/#Magnesium oxide 4 Arron/vers Patented Nov. 23,1948 METHOD F MAKING DENSE MAGNESIUM 0\XIDE Alvin n. Dahl, manahmen.,minor i0 The N Dow Chemical Company, corporation of Delaware Midland,Mich., a

Application March 13, 1947, Serial No. 734,325

' l The invention relates to a method of making magnesium oxide in' adense form. It more parl claim. (ci ca -co1) ticularly concerns a methodof making magnesium oxide by reacting magnesium and oxygen. whereby thereaction product is obtained in the molten state and subsequentlysolidified in a i dense form.

The principal object of the invention is to provide a method of makingmagnesium oxide which is dense and hard and possesses high electricalresistance, a combination of properties which renders the materialuseful in the electrical lndustry, OtherI ,objects and advantages willappeal' as the description proceeds.

I have vfound that by introducing molten globules of magnesium into anatmosphere of oxygen the molten. magnesium burns quietly and the productof the burning is magnesium oxide largely in molten form rather thandust or fume. On cooling the magnesium oxide so produced, it

y solidines to an unusually dense crystalline product most of which istranslucent to transparent. In addition it is highly electricallyresistant so that it is useful in the electrical industry especialiy forinsulating electrical resistance heating elements that are encased inmetallic sheaths.

The invention, then, consists of the method hereinafter-more fullydescribed and particularly pointed out in the claims, the followingdescription and accompanying drawing setting forth a preferred mode ofcarrying out the invention,

such as mode illustrating, however, but one of the various ways in whichthe invention may be practiced.

In the drawing, Fig. 1 is a schematic view largely in section or a sideelevation of an apparatus with which the method may be practiced. Fig. 2is a horizontal cross section on the line 2--2 of Fig. 1.

As shown in the drawing, the apparatus comprises a refractory base iacross the upper portion of which is formed a trough 2. Slidably httingthe ends of the trough are the removable refractory closure blocks 3provided with handles t. The inner ends 5 and 6 of the blocks and theportions l and 8 of the trough comprise the sides, and the portion 9 ofthe trough comprises the bottom, of the hearth I0. A lateral passage I iis formed yin the base I, providingcommunication to the hearth for theintroduction thereinto of oxygen. A refractory tower I2 having an axialfurnace shaft I3 or combustion zone is disposed vertically above thehearth I 0. A vent H is provided near the upper end II of the tower. Therefractory portions of the foregoing apparaits position and thus that`gradually forms a preferably of magneslte brick. I5 onthe upper end ofthe shaft p'ot or crucible IB (preferably of adapted to melt and hold aquanmagnesium. A valved aperture I 'I is provided in the bottom of thecrucible centrally disposed over the shaft I3. A jacket l0 is arrangedaround 'the melting pot so as to provide a heating zone I9 surroundingthe sides of the crucible I6 for combustion gases delivered from theburner 20 through the port 2l. The size of the passage through theaperture I1 is regulated by the cone shaped valve 22 which is mounted onthe lower end of the valve s'tem 23. Regulation of the valve isaccomplished by the weighted lever 24 which is pivoted on the support 25attached to the melting pot. As shown, on one end of the lever 24 ispivoted the upper end 23 of the valve stem 23, on'the otheris a weight21 .capable oi.' overbalancing the weight of the valve and valve stem.Screw means 28 threaded through the extension 29 of the support 25engages the lever arm at 3i) to regulate of the valve 22.

The operation of the method will be best understood from the followingdescription in which magnesium `is oxidized with gaseous oxygen toproduce a solidified fused magnesium oxide, the fusin resulting from theintense heat of the oxidation reaction. In carrying out the method usingthe apparatus illustrated, a quantity of' magnesium metal is chargedinto the crucible I6 and its temperature maintained above the meltingpoint -oi magnesium l(651o C.) .by the burner 20, valve 22 being in thedown position so as to close aperture I 'I as by adjusting screw means28 upwardly to a suitable level. A stream of oxygen is admitted topassage Ii from which it flows into the hearth I0 and upwardly therefrominto the shaft I3. Screw means 28 is then turned slowly so as to raisevalve 22 until a dropwise flow of molten magnesium is released fromaperture I 'i into the combustionshaft I2 where it is met by theascending oxygen. Upon coming into contact with the oxygen, themagnesium globules rapidly'oxidize or burn with a white flame producinga large amount of heat at a sufficiently high temperature to fuse themajor tus are made Upon the plate rests a melting steel) which is tityof molten portion of thc resulting magnesium oxide which forms largeenough masses to fall readily to the floor 9 of the hearth III while asmall proportion escapes as lfume or dust through the vent I4. As thefused magnesium oxide falls, it cools and pile of solidified fusedproduct fused product that is collected 3|. The solidified be removed byremoving the closure blocks ii and pushing the pile beyond one end orthe other of the trough 2. Following removal, the product may becrushed; if desired to form a granular product of desired mesh size.

Various rates of flow of either the molten metal or oxygen arepermissible, however, if the proportion of oxygen to magnesium is lessthan that called for by stoichiometrical proportions given in theequation:

on the hearth may l and there is only a small loss of magnesium oxide asdust or fume since the major portion forms coarse granules and largermasses.

Inasmuch as there is a tendency for the oxidation of the magnesium tobegin immediately the metal enters the oxygen atmosphere below theaperture, oxide may accumulate about and in the aperture and interferewith the dripping of the molten metal into the combustion zone of theshaft I3 on prolonged or repeated use of the apparatus. This diiilculty,I have found, may be overcome by introducing helium, or other gas inertto magnesium, into the upper end of the shaft I3 in the vicinity of theaperture I1 so as to displace oxygen from immediate contact therewith.This may be accomplished by directing a small stream of helium gastoward the aperture I1 as by means of a tube 3i inserted through thevent I4 so that the discharge end 32 is positioned in the shaft space inthe vicinity of the aperture as shown. Y

'I he length of travel of the magnesium globules in the shaft I3 duringcombustion and hence the duration of the time of contact between themagnesium globules and the oxygen necessary to obtain complete oxidationof the magnesium is comparatively small. For example, in one set oftests, I found that a free fall of about 9 inches in an oxygenatmosphere preheated to 800 C. was suiiicient to burn completely eachglobule of molten magnesium. In practice, the free fall may be made longenough to provide for both complete oxidation and cooling of the oxideproduced. For example, I have found that a shaft, height giving a freefall to the globules of '7l/2 feet is ample both for oxidation andsubsequent cooling. I

Although I have illustrated in the drawing the passage of the oxygen incountercurrent flow to the descending globules of molten magnesium, Ihave found that the oxygen may be introduced into the shaft through thevent I4 instead of the passage II, thereby flowing the oxygen and themagnesium in the same direction. When adopting such mode of operation,the passage II serves as s. vent.

It will ne understood that very high temperoperation as by directing anair blast against the outer surface or embedding cooling means in therefractory workof the shaft itself.

Fused magnesium oxide produced by the foregoing method and then crushedso as to pass a 40 mesh standard sieve lbut not a 300 mesh standardsieve has a bulk density of about 2.4 to 2.6 grams per cubic centimeterand a very high electrical resistance.

I claim:

1. The method of making magnesium oxide in solidified fused form whichcomprises introducing globules of molten magnesium into an atmosphere ofoxygen whereby the globules burn forming magnesium oxide, said globuleshaving a free fall of suicient duration in the said atmosphere of oxygento complete their oxidation.

2. The method of making magnesium oxide in solidified fused form whichcomprises dripping molten magnesium into an atmosphere of oxygen wherebythe drops of magnesium burn forming fused magnesium oxide, andsolidifying and co1- lecting the resulting magnesium oxide product.

3. The method of making magnesium oxide in solidified fused form whichcomprises dripping molten magnesium into an atmosphere of oxygen wherebythe drops of magnesium burn forming fused magnesium oxide, introducingoxygen into the said oxygen atmosphere at a rate 30 to per cent, greaterthan that corresponding to the stoichiometrical proportions of magnesiumand oxygen, and solidifying and collecting the resulting magnesium oxideproduct.

4. The method of making magnesium oxide in solidified fused form whichcomprises dropping molten globules of magnesium into an upwardiy movingcolumn of oxygen, the oxygen being about 30 to 'I0 per cent in excess ofthe stoichiometrical proportion to magnesium, whereby the magnesiumburns to magnesium oxide, and collecting theresulting product.

5. The method of making magnesium oxide in solidified, fused form whichcomprises introducing magnesium into an atmosphere of oxygen highlyheated by the burning therein of previously introduced magnesium wherebythe magnesium burns forming fused magnesium oxide, supplying additionaloxygen to the said oxygen atmosphere at a rate 30 to 70 per cent greaterthan that corresponding to the stoichiometrical proportionsof magnesiumand oxygen, solidifying and collecting the resulting magnesium oxideproduct, and introducing into the said oxygen atmosphere in the vicinityof the point of introduction of the said magnesium a gas inert to themagnesium whereby oxidation of the magnesium a-t the point ofintroduction is prevented.

ALVIN D. DAHL.

No references cited.

